Simple fade-in fade-out screen transition for libGDX

TransitionScreen.java

package leo.sortorsplode;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Screen;
import com.badlogic.gdx.graphics.glutils.ShapeRenderer;

public class TransitionScreen implements Screen {
	private Screen currentScreen;
	private Screen nextScreen;

	private SortOrSplode game;

	// Once this reaches 1.0f the next scene is shown
	private float alpha = 0;
	// true if fade in, false if fade out
	private boolean fadeDirection = true;

	public TransitionScreen(Screen current, Screen next, SortOrSplode game) {
		this.currentScreen = current;
		this.nextScreen = next;

		// I temporarily change the screen to next because if I call render() on it without calling the create() function
		// there will be crashed caused by using null variables
		game.setScreen(next);
		game.setScreen(current);

		this.game = game;
	}

	@Override
	public void show() {

	}

	@Override
	public void render(float delta) {
		Gdx.gl.glClearColor(0, 0, 0, 0);
		Gdx.gl.glClear(Gdx.gl.GL_COLOR_BUFFER_BIT);

		if (fadeDirection == true) {
			currentScreen.render(Gdx.graphics.getDeltaTime());
		} else {
			nextScreen.render(Gdx.graphics.getDeltaTime());
		}

		Gdx.gl.glEnable(Gdx.gl.GL_BLEND);
		Gdx.gl.glBlendFunc(Gdx.gl.GL_SRC_ALPHA, Gdx.gl.GL_ONE_MINUS_SRC_ALPHA);
		game.shapeRenderer.setColor(1, 1, 1, alpha);
		game.shapeRenderer.begin(ShapeRenderer.ShapeType.Filled);
		game.shapeRenderer.rect(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
		game.shapeRenderer.end();
		Gdx.gl.glDisable(Gdx.gl.GL_BLEND);

		if (alpha >= 1) {
			fadeDirection = false;
		}
		else if (alpha <= 0 && fadeDirection == false) {
			game.setScreen(nextScreen);
		}
		alpha += fadeDirection == true ? 0.01 : -0.01;
	}

	@Override
	public void resize(int width, int height) {

	}

	@Override
	public void pause() {

	}

	@Override
	public void resume() {

	}

	@Override
	public void hide() {

	}

	@Override
	public void dispose() {

	}
}

It does not even need FBOs or Scene2D

Where does the member "shapeRenderer" come from?